This invention relates to an improved method for conducting a chemical process in a multi-tubular vessel containing a plurality of packed vertically arranged tubes. In particular, this invention relates to an improvement in conducting a process in such a vessel in which a feed which contains at least one liquid is introduced into the vessel and in which at least one liquid product and at least one gaseous product are obtained. In such processes, the gaseous product may be, for instance, a gas which had been also introduced as a feed or which was dissolved in the liquid and is recovered as a vapor from the vessel, a liquid introduced as feed which becomes vaporized during the conduct of the process, or a gas produced by a chemical reaction of the liquid feed or between the liquid feed and another reactant introduced. Similarly, the liquid product obtained may be a portion of the liquid feed which, for instance, was not reacted in the vessel, or a liquid product obtained by reaction of the liquid feed with another reactant.
Examples of processes which may be generally carried out in packed multi-tubular reactors are those which are exothermic or endothermic such as hydrocarbon reforming, cyclization, dehydrogenation, desulfurization and dehydration. The packing may include one or more catalysts know to effectuate such reactions.
Generally, heat transfer to or from the tubes is accomplished through the use of gaseous or liquid heat transfer fluid in the shell space surrounding the tubes.
When operating such chemical processes in vessels containing a plurality of vertically arranged packed tubes, generally speaking, one of two methods of operation are utilized, which are illustrated in FIGS. 1 and 2.
According to FIG. 1 a liquid feed is introduced in line 1 into a vessel or reactor 2 which contains a plurality of vertically arranged packed tubes 3. The liquid feed, optionally together with other feeds, is forced to flow downwardly through the tubes and the packing contained therein, and all products, liquid and gaseous, are removed from the lower portion of vessel 2 via line 4. The liquid and gaseous products contained in line 4 are then sent for further processing. One example of such is shown in FIG. 1, in which the liquid and gaseous products in line 4 are introduced into a liquid/gas separator 5, with gaseous product being removed via line 6 and liquid product via line 7.
A second method of operation of such processes is depicted in FIG. 2. In this technique, a feed containing at least one liquid is introduced via line 10 into a vessel or reactor 11 containing a plurality of vertically arranged packed tubes 12. The feed, and products produced therefrom, are forced to flow upwardly through the tubes 12 and are removed at the upper portion of the vessel in line 13. As in FIG. 1, these products in line 13 are transmitted for further processing, for instance, passed into a liquid/gas separator 14 from which gaseous product is removed via line 15 and liquid product in line 16.
One example of a process conducted as in FIG. 2 is described in U.S. Pat. No. 3,230,055, which describes an apparatus and method for continuously contacting a gas and liquid in predetermined proportions, particularly for carrying out liquid/gas phase chemical reactions.
Another process of such type is described in U.S. Pat. No. 4,119,659, which pertains to a process for producing a series of chlorothioformate compounds by reaction of a mercaptan with phosgene.
Conducting processes by means such as described above and in FIGS. 1 and 2 possesses certain disadvantages, particularly associated with lack of uniformity of distribution (and reaction) in the various tubes of the vessel and possible lack of good heat transfer (either addition of heat to or removal of heat from the tubes).
For instance, when operating with forced downflow and removal of all products from the lower portion of the vessel as in FIG. 1, the tubes will function as miniature trickle bed reactors because of the gases produced. This results in considerably less efficient transfer of heat to or from the tubes than is desired. In addition, liquid may flow more rapidly into and down the tubes located closer to the liquid inlet or inlets then tubes located further away. In such operations, therefore, there may be a lack of uniformity of conditions from tube to tube, and a somewhat inefficient use of tubes, since some will carry more of the process load than others. Transfer of heat to or from tubes will similarly be nonuniform and thus generally less efficient. This may result in poor control of this reaction; the yield may be reduced, and/or undesired by-products may be formed.
Additionally, if the process to be conducted is one which involves a comparatively long reaction, the reactants may flow through the tubes too quickly, and reaction may not be complete.
Operation of such process according to FIG. 2, that is with introduction of liquid feed into the lower portion of the vessel and removal of liquid and gaseous products from the upper portion, can result in improved performance. Howwever, there may still be a nonuniform utilization of the tubes in the vessel. If for any reason the rate of reaction varies from tube to tube, an imbalance may occur. The tubes with the most reaction, and therefore the greatest rate of gas generation, will have the lowest pressure drop, which is dependent on the proportion of gas to liquid within each tube. More feed therefore will flow to these tubes, which then generate gas faster, and experience a temperature rise, and because of the low pressure drop, liquid will feed quicker to these tubes than to the others. The result can be that the flow rates may vary widely from tube to tube, with some tubes having very high flow rates, while others, very low ones, possibly extending to zero or negative flow rates (i.e., liquid circulates downwards rather than upwards).
In either type of process according to the prior art, nonuniform distribution and flow of materials through the tubes can result in lower than desirable conversion of liquid feed to desired product, and possibly increased production of unwanted by-products. Control of temperature and heat transfer to and from tubes becomes more difficult. Temperatures can vary from tube and affect efficiency and heat utilization of processes in general. If the reaction being conducted is temperature-sensitive, undesirable or less advantageous operational results can occur.
It is an object of the present invention to provide an improved method for operating a chemical process in a vessel or reactor containing a plurality of vertically arranged packed tubes, in which a liquid feed is introduced into the vessel, and in which at least one liquid and at least one gaseous product are obtained, which improves the performance of the process with respect to stability and uniformity of distribution of materials through the tubes and uniformity of heat transfer.
A secondary objective of this invention is to provide such an improved process for use in the production of chlorothioformates which are liquids, by reaction of a liquid mercaptan with phosgene, which may be in liquid or gaseous form, and in which gaseous products such as hydrogen chloride and optionally phosgene are obtained.